JPH04189068A - Image forming device - Google Patents

Abstract

PURPOSE:To obtain a recording picture element with high picture quality by providing a gradation processing section growing a dot in order from a dot corresponding to a minimum recording picture element position with high priority and preventing the dot with specific priority from completely being grown to the device. CONSTITUTION:A gradation conversion table 23 uses an input picture signal 25, a horizontal binary counter output 24, and a vertical binary counter output 29 as memory addresses and has a picture element level on its own table after gradation conversion. An address line consists of 10 bits, a signal 25 is allocated to high-order 8 bits, an output 29 is allocated to a 9-th bit, and an output 24 is allocated to a 10th bit. When the signal 25 consists of 8 bits (256 levels), since four gradation characteristics are provided, in total 1024 addresses are obtained. That is, the device is controlled such that the picture element is grown while providing priority to each picture element in a segmented picture block and growing of the picture element with specific priority is suppressed.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of the Invention The present invention relates to an image forming apparatus for obtaining high quality recorded images.

2. Description of the Related Art Printers based on various principles have been proposed as output terminals for personal computers, workstations, and the like. In particular, laser beam printers (hereinafter abbreviated as LBP) that use an electrophotographic process and laser technology are superior in terms of recording speed and print quality, and are rapidly becoming popular.

On the other hand, demand for full-color LBPs is increasing in the market, but in the case of full-color LBPs, image data is output in addition to conventional characters and line drawings.
- It is necessary to perform image processing on the premise of multi-level output for digital LBP binary data processing.

In the case of image output equipment that supports electrophotographic processes such as the LBP mentioned above, there is a problem with the stability of the electrophotographic process itself, so the number of stable gradations that the electrophotographic process itself has is at most 3.4 gradations. That's about it.

Today, the binary dither method is often used as a method for recording halftone images in image output devices with an insufficient number of output gradations, such as LBPs and ordinary thermal transfer printers. However, the binary dither method requires the use of a dither matrix of a much larger size in order to obtain sufficient gradation, resulting in a decrease in resolution and the occurrence of moiré due to interference between the halftone dots of the original and the dither pattern. There were problems such as image quality deterioration.

A multilevel dither method has been proposed to improve the above problems. The multilevel dither method will be explained using FIG. 10. To simplify the explanation, it is assumed that the image data has already been stored in the image memory 101.

Image memo +7101 stores R, G, and B brightness data, each with 8 bins per pixel)X3=2
It has 4 bits of information. These pixel data are stored in a main scanning direction counter 102 and a sub-scanning direction counter 1.
03, and all R, G, and B are read out from the beginning.

Since these R, G, and B are luminance signals, the density converter 10
4, density conversion is performed to obtain density signals C and M.

Convert to Y (three primary colors for printing). This conversion is usually done in ROM
Alternatively, the contents are accessed using a data value stored in a RAM or the like as an address. The actual table contents are, for example, the 11th
Values based on the conversion characteristics shown in the graph in the figure are written.

The density-converted pixel data is sent to the color correction unit 105 for all three colors.
The 0 color correction unit 105 inputs the density data to UCR/black plate generation, masking, etc., which are well-known techniques, are performed on the density data. Black is added to the image data by the color correction unit 105, and the amount of information per pixel is effectively 8×4=32.
It has become Bi-Ato. Next, these four color data are transferred by the data selector 107, for example, if the transfer destination is the engine of a full color printer, Bk, C.

Data is transferred sequentially in M and Y planes.

On the other hand, among the address outputs of the main scanning direction counter 102 and the sub-scanning direction counter 103, the lower 3 bits of each (3 bits) are connected to a storage device 107 for storing a dither threshold matrix, and a threshold value uniquely determined by the spatial coordinates of the image is stored. The address that accesses the storage device 107 has a total of 6 bits, that is, it is possible to access 64 pieces of data.In this case, the dither threshold matrix stored in the storage device 107 is, for example, as shown in FIG. 8
A ×8 dither threshold matrix or the like can be considered.

The threshold value output from the storage device 107 is sent to the comparator 108.
It is compared with the lower 6 bits of the 8 bits of density data output from the data selector 106. If the density data is greater than or equal to the threshold value, the comparator 108 outputs, for example, l as the comparison result. Also, if the density data is smaller than the threshold, for example, 0 is set as the comparison result 11
Output as 1.

On the other hand, the upper two bits of the density data output from the data selector 106 are connected to a storage device 109 for re-determining pixel values, and together with the comparison result 1 bit output from the comparator 108, a total of 3 bits of data are stored. is accessed and the final output value 112 is output.

FIG. 13 shows an example of the final output value when the upper two bits of the output of the data selector 106 are the density level signal 110, and the comparison output of the comparator 10g is the comparison result 111.

The above explanation is a method taken when implementing a multilevel dither into hardware, and as shown in FIG. It becomes dayza.

In general, when outputting a full-color image using an image output device with a small number of multi-value levels, multi-value dither methods such as those shown here are widely used. For example, the number of gradations that can be output by the image output device itself is 4. However, if a relatively large dither threshold matrix such as 8×8 is combined, 8×8×(4,−1)+1=193 gradations can be obtained by pseudo gradation.

Problems to be Solved by the Invention However, for image output devices such as conventional LBPs and thermal transfer printers, which have a small number of gradations in the process or transfer principle itself, pseudo-area gradation techniques, including multilevel dither methods, cannot be used. Widely used.

These can be achieved by devising a halftone type dither threshold matrix (to prevent multiple dots from concentrating in one matrix, and adopting a threshold matrix that aims to achieve both resolution and gradation), or by using image output equipment. It has become possible to obtain a certain degree of image quality by improving the resolution of the minimum recorded dot or by irregularly switching the dither matrix depending on the density level.

However, even in the case of multilevel dithering, deterioration in resolution is unavoidable when it is desired to increase the number of gradations, and in principle, an intermediate density level is used within one pixel, which tends to cause density unevenness in the recorded image.

In addition, although low gradation areas require smoothness due to visual characteristics, they only have a few extreme density levels, so when the lowest density recording pixels are formed on a white background, there is a feeling of roughness. and texture, which deteriorates image quality, especially in low gradation areas.

Furthermore, as image quality improves, it may be necessary to separately prepare a dither matrix that describes rules different from the regular rules for so-called dots, where adjacent dots on all sides are safely fused after heat fixing. In this case, it is essentially difficult to avoid deterioration in character quality when the characters are treated as line drawings or images, for example, and there are limits to image quality improvement.

Therefore, an object of the present invention is to provide an image forming apparatus that can solve the above problems.

Means for Solving the Problems For this purpose, the present invention sets a block consisting of a plurality of pixels on transmitted or stored image data, and within this block, according to a spatially predetermined priority order, high priority The dots are grown in order from the dot corresponding to the minimum recording pixel position, and the dots with a specific priority are suppressed from growing completely.

Effects In the above configuration, the dots are grown purely from the dots corresponding to the minimum recording pixel position with a high priority, and by suppressing the complete growth of dots with a specific priority, excellent gradation and reproduction characteristics are achieved. High quality recorded images can be obtained.

EXAMPLES Next, the present invention will be described in detail with reference to the drawings. FIG. 1 shows a schematic diagram of an image forming apparatus.
In the figure, reference numeral 1 denotes a digital data output device, which inputs image signals from an image scanner, video camera, etc. (not shown), and performs predetermined image processing using an A/D converter. The image data may be temporarily stored in a memory, or may be an interface for image signals from a direct communication means.

When the print engine 19 starts up, the digital data output device 1 starts transferring digital image data to the image processing section 2. The data to be subjected to image processing is 24 bits in total, 8 bits for each color of RGB. The RGB data input to the image processing section 2 is luminance data, and the density conversion section 3 converts the luminance data into density data, that is, CMY (cyan, magenta, yellow), which are the three primary colors of printing.

In general, this change can be easily achieved by writing the conversion table data 4 on a storage device such as RAM-ROM, and accessing it by appropriately offsetting the input data value. Density, overall density, contrast, background color control, etc. (density and color adjustment) can be performed.

The RGB (luminance) data has been converted to a degree conversion viCM Y (density) data 5, 6, and 7, and then UCR (undercolor removal) and black plate generation 8 are performed using the CMY data. U
CR reduces data at a constant rate with respect to the common amount of CMY data. Basically, this reduction amount is generated as a black plate.Originally, the purpose of OCR and black plate generation is to replace the common amount of CMY with black on a pixel basis and save coloring material (toner). .

However, today, UCR and black plate generation are rarely performed purely to save toner, but rather to prevent gradation deterioration in high-density areas, ensure contrast, and ensure gray balance in high-density areas, etc. After generating OCR and black plates using the above processing, it is possible to output even higher quality images by actively changing the amount of UCR and black plates.
C data 9, M data io, y data 11, and Bk (black) data 12 are generated.

Thereafter, data other than Bk data 12, which is an achromatic color component, is input to the color correction section 13. The color correction unit 13 performs processing such as masking on the colored components (CMY). The purpose of masking is to correct the influence of unnecessary absorption bands of each white coloring material. For example, C (cyan) coloring material has unnecessary absorption bands in wavelength regions other than C. Specifically, it has a Y (yellow) color component, for example.

Similarly, Y is included in M (magenta). Therefore, when recording Y, it is necessary to reduce the Y component contained in C and M according to the density at which C and M should be recorded.
The method is usually 3X3 for CMY digital signals.
The matrix calculation or the calculation result is written in a storage device such as a ROM, and after each color is accessed, addition and subtraction are performed to obtain the result.

Conventionally, 3x3 linear masking (first-order masking) has been the mainstream, but first-order masking is insufficiently effective, and recently more than two-order nonlinear masking, or mapping that performs color correction itself within a black box, has been used. Considering this, many new color correction methods that calculate mapping functions in areas other than CMY space have been proposed.

The color correction unit 13 inputs the input data C data 9 and M data 1.
0, Y data 11, C' data 14, M' data 15,
It is converted into Y' data 16.

On the other hand, since the Bk data 12 is achromatic data, it is not involved in color correction.

The C' data 14, M are subjected to color correction by the color correction section 13.
'Data 15, Y' data 16 (colored data) and Bk
Data 12 (achromatic color data) is such that only one color data is selected by the data selector 17, and is input to the gradation processing section 18, where the gradation processing of the image signal related to the present invention is performed.

The image signal subjected to gradation processing is sent to the printer engine 19, and a high-quality recorded image, which is the object of the present invention, is obtained.

Here, the contents of the gradation processing related to the present invention will be explained in detail using FIG. 2. Figure 2 shows the gradation processing section 1 in Figure 1.
8, 20 in FIG. 2 is a horizontal synchronizing signal generating circuit, which outputs a horizontal synchronizing signal 21 for an image. In the case of a laser beam printer, for example, a beam detect signal from a laser scanning optical system (not shown) can be used as a generation source of the horizontal synchronization signal 21 by applying waveform shaping or the like. 22 in Figure 3 is horizontal 2
It is a forward counter that counts the horizontal synchronization signal 21, and outputs 0N-O every time this horizontal synchronization signal 21 is input.
FF is replaced.

Reference numeral 26 in FIG. 2 is a vertical synchronization signal generation circuit, which outputs a vertical synchronization signal 27 for an image. For example, a data transfer lock can be used as is as a generation source of the vertical synchronization signal.

28 in FIG. 2 is a vertical binary counter which counts the vertical synchronizing signal 27, and the output is switched between ON and OFF every time the vertical synchronizing signal is input.

To explain each of the above signals in more detail, FIG. 4 shows changes in the horizontal synchronizing signal 21, vertical synchronizing signal 27, horizontal binary counter output 24, and vertical binary counter output 29 in the time axis direction. The horizontal synchronization signal 21 is generated at the beginning of line data once every transfer of one line of data (line period).
The vertical synchronization signal 27 corresponds to each data in the l line (
The number of occurrences is equal to the number of pixels included in the l line. If each of these signals is counted by a binary counter, the horizontal binary counter output 24 and the vertical 2
There are four combinations of the advance counter outputs 29.

As shown in Figure 4, horizontal binary count output = 0, vertical 2
When the binary counter output = 0, state A; when the horizontal binary counter output = 1; when the vertical binary counter output; O, state B; when the horizontal binary counter output = 0, and the vertical binary counter output = 1 State C1 If the time when the horizontal binary counter output = 1 and the vertical binary counter output = 1 is defined as the state, the state of each counter output corresponds uniquely depending on the spatial position of the pixel, and each pixel The states of the counter outputs corresponding to the positions are classified into state A, state B, state C1, and state D, as shown in FIG.

Hereinafter, if the symbols A, B, C, and D are used as symbols to indicate pixel positions regularly arranged in space, the entire image will be composed of 2 × 2 pixels consisting of pixels at positions A, B, C, and D. It can be divided into two areas.

Reference numeral 23 in FIG. 2 is a gradation conversion table, which has the input image signal 25, horizontal binary counter output 24, and vertical binary counter output 29 as memory addresses, and has pixel levels after gradation conversion in the table. The address line is composed of 10 bits, of which the input image signal 25 is assigned to the lower 8 bits, the vertical binary counter output 29 is assigned to the 9th bit, and the horizontal binary counter output is assigned to the 10th bit.

Here, the gradation conversion table 23 will be explained in more detail using FIGS. 5 and 6. FIG. 5 shows the contents of the gradation conversion table.

If the input image signal is 8 bits (256 levels), 1
256 addresses are required in the table to determine the gradation characteristics for one pixel, and in this example, there are 4 gradation characteristics classified as A, B, C, and D, so a total of 1024 addresses are required. becomes.

In other words, data representing the gradation characteristics for the pixel at position A is stored at address 5 0OOH-OFFH, and at address 100
H-IFFH stores data representing the gradation characteristics of the C position, addresses 200H-2FFH store data representing the gradation characteristics of the B position, and addresses 300H-3FFH store data representing the gradation characteristics of the D position. has been done.

FIG. 6 is a graph showing the tone conversion characteristics in the example. In this embodiment, the priority of the pixel at the A position is set to the highest, followed by the B position, the C position, and the D position is set to the lowest priority. Furthermore, the gradation characteristics of the pixels at the human position and the C position are set so that the pixels are recorded at a predetermined density below the saturation density so that the pixels do not grow completely.

Regarding the gradation characteristics corresponding to the pixel position with the highest priority in the A position, the output increases continuously as the input image level increases from OOH to 3FH, but when the input image level exceeds 3FH, the output increases to BFH. Affirmed.

The gradation characteristic corresponding to the pixel position with the next highest priority after the B position is 00H when the input image level is less than 3FH.
The output increases continuously from 3FH to 7FH, and when the input image level exceeds 7FH, the output is fixed at FFH.

The gradation characteristic corresponding to the C position, that is, the pixel position with the next highest priority after the B position, is 00H when the input image level is less than 7FH.
The output increases continuously as the input image level increases from 7FH to BFH, and when the input image level exceeds BFH, the output is fixed at BFH.

The gradation characteristic corresponding to the pixel position with the lowest priority in position D outputs 00H when the input image level is BFH non-vortex.
As the input image level increases from BFH to FFH, the output increases continuously and reaches FFH.

That is, a priority is given to each pixel in the cut-out image block to cause the pixel to grow, and control is performed to suppress pixel growth for pixels with a specific priority.

Setting priorities as described above in pixel formation means that in electrophotographic printers, it is better to give priority to the growth of specific pixel dots on the photoreceptor than to grow the dots of each pixel uniformly. A strong electric field is generated in the micro region of the electrostatic latent image, improving the gradation of the recorded image.

In general, in a natural image, the correlation between adjacent pixels is very high, so by following the method of this embodiment, it is possible to easily give priority, that is, difference, to the pixel growth within a block, and the gradation can be adjusted at the latent image level. Improves sexual performance. Not only that, but because a specific spatial frequency component is superimposed on the image as a result, resistance to, for example, drive unevenness caused by the drive system is improved. In other words, the method of the present embodiment is a novel method of superimposing noise having a specific spatial frequency component on an image, and the method is a novel method of superimposing noise having a specific spatial frequency component on an image. It is not affected by the periodic threshold value and is close to the analog of the pixel (for example, 256
A major feature of this method is that it originates from the density level itself (gradation), and is significantly different from conventional gradation reproduction methods such as dither methods that provide discrete noise levels (for example, 4 gradations).

In other words, in this embodiment, the exact order in which pixels in a block grow is not guaranteed9.For example, even if the highest priority pixel does not grow completely within one block, the lowest priority pixel pixels may grow. Particularly in images with undulating data, for example, in portions of the image such as characters and line drawings with steep edges, the growth levels of pixels may be reversed depending on how the blocks are arranged.

That is, the priority in this embodiment does not determine the growth order of pixels, but merely defines the input density level at which each pixel grows. However, in directional natural images, although the correlation between adjacent pixels is very high, tone reproduction is affected to some extent depending on the input density level in a spatially macro area (
The same effect as if the pixels (in the growth stage) were selected and the growth order was defined as a result is obtained.

Also, the fact that the order of pixel growth is not completely determined means that resolution deterioration can be minimized by some method, for example,
In methods that process pixel data within a block and rearrange the data by assigning priority to each pixel position, pixel data does not actually exist (or its value is small)
There is a possibility that data is weighted by location, and the resolution is definitely degraded.

However, in the method of this embodiment, even if the pixel value is large enough for a line drawing, for example, and the density is high (most of the time, text and line drawings are output at maximum density), the target pixel will definitely grow. The resolution will not deteriorate at all.

Furthermore, with the method described in this embodiment, almost analog-like density control can be performed in all density regions due to visual characteristics, so high-density recording dots do not suddenly appear on a white background, and especially smooth images such as natural images, etc. It is possible to suppress roughness in low gradation areas of an image and to significantly improve gradation properties in low gradation areas.

In other words, this method emphasizes gradation, especially in low-gradation areas, for smooth images, and emphasizes resolution for areas that are usually expressed in high density, such as characters and line drawings. It shows the characteristics.

In addition, since pixel growth is suppressed for some priority pixels in the block, black blurring in high density areas is effectively reduced (
As a result, the gradation in the high density region is improved.

For example, when performing gradation expression by setting priorities for four pixels, the method described above can either not completely grow the pixel with the highest priority, or completely grow the pixels other than the pixel with the lowest priority. It is also easy to change not to let it grow. That is, the targets for pixel growth suppression can be set in any number, with any priority, and at any position. These changes can be made very easily by simply changing the contents of the gradation conversion table.

Further, although this embodiment has been described in detail by setting 2×2 blocks, the present method can be applied regardless of the block size. This change changes the number of count bits of the counter according to the size of the block (it doesn't matter if the size in each direction is different), secures a gradation conversion table area for the number of output states of the counter, and This can be achieved by simply writing the contents of the conversion table.

Next, a laser beam printer employing the gradation processing described in this embodiment will be described in detail with reference to FIGS. 7 to 9.

Laser beam printers, which form color images by applying electrophotographic process technology, selectively irradiate light beams corresponding to each color onto a photoreceptor having a photosensitive layer to form an image. A method is adopted in which multiple electrostatic latent images, each corresponding to a specific component, are developed with respective predetermined toners, and these monochrome toner images are superimposed to form a color image on a single sheet of transfer material. There is.

FIG. 7 is a side sectional view of the laser beam printer, FIG. 8 is an explanatory diagram of the operation of photoconductor reference detection, and FIG. 9 is an explanatory diagram of the operation of intermediate transfer member reference detection.

In FIG. 7, the third step is selenium (Se) on the outer peripheral surface of the belt base material such as resin on the closed loop having the seam 31a.
Alternatively, it is a photoreceptor on which a photosensitive layer such as an organic photoconductor (OPC) is applied in the form of a thin film.

The photoreceptor 31 is supported by two photoreceptor transport rollers 32.33 such that a vertical plane is formed between the photoreceptor transport rollers 32.33, and the photoreceptor transport rollers 32.33 are driven by a drive motor (not shown). It rotates in six directions along the arrow. A charger 34, an exposure optical system 35, black (B), cyan (C), magenta (M), and yellow (Y) are installed on the circumferential surface of the photoreceptor 31 on the belt in the order of the rotation direction of the photoreceptor shown by arrow A. Developers for each color 36B, 36C136M, 36
Y, intermediate transfer unit 37, photoreceptor cleaning device 38. A static eliminator 39 and a photoreceptor reference detection sensor 40 are provided.

The charger 34 is a charging wire 41 made of tungsten wire or the like.
, a temporary shield 42 made of a metal plate, and a grid plate 43. By applying a high voltage to the charging wire 41, the charging wire 41 causes corona discharge, and the photoreceptor 31 is uniformly charged via the grid plate 43. 44 is an exposure light beam for image data emitted from the exposure optical system 35.

Laser beam printers use this exposure light! ! Reference numeral 44 is obtained by applying an image signal from a gradation conversion device to a semiconductor laser (not shown), which is light intensity modulated or pulse width modulated by a laser drive circuit (not shown), and is applied to a semiconductor laser (not shown). A plurality of electrostatic latent images each corresponding to a specific component among a plurality of predetermined color components are formed.

As shown in FIG. 8, the photoreceptor reference detection center 40 detects the position of the seam 31a of the photoreceptor 31.
At one end of the photoreceptor 31, the seam 31. A photoreceptor reference mark 31b such as a slit placed at a predetermined position with respect to a is detected.

Each color developing device stores toner corresponding to each color. The selection of the toner color is performed using separation cams 45B and 4, which correspond to each color and whose both ends are rotatably supported on the main body of the machine.
5C145M, 45Y rotate in response to the color selection signal,
This is carried out by bringing a selected developing device, for example 36B, into contact with the photoreceptor 31. The remaining unselected developing devices 36C, 136M and 36Y are spaced apart from the photoreceptor 31.

The intermediate transfer body unit 37 includes a seamless loop belt-shaped intermediate transfer body 46 made of conductive resin or the like, and two intermediate transfer body conveyance rollers 47 that support the intermediate transfer body 46.
．． 48 and the photoreceptor 31 with the intermediate transfer member 46 in between in order to transfer the toner image on the photoreceptor 31 to the intermediate transfer member 46.
The intermediate transfer roller 49 is arranged opposite to the intermediate transfer roller 49 . Here, the surface circumference L1 of the photoconductor 310 is the intermediate transfer body 46.
is nominally equal to the surface circumference L2, but is set so that the relationship L1≦L2 always holds within the range of variation.

Next, as shown in FIG. 9, reference numeral 50 denotes an intermediate transfer body reference detection sensor for detecting the reference position of the intermediate transfer body 46, and an intermediate transfer body reference mark such as a slit placed at one end of the intermediate transfer body 46. The reference position is detected at 46a.

51 is a photoreceptor clutch mechanism, and a driving source (not shown)
It is provided on the drive shaft of the photoreceptor conveying roller 33, and controls the rotation of the photoreceptor by adjusting the power from the roller 33 to 0N-OFFL. Reference numeral 52 denotes an intermediate transfer body cleaning device for scraping off residual toner on the intermediate transfer body 46, and the intermediate transfer body 46 is cleaned while a composite image is being formed on the intermediate transfer body 4G.
It is spaced apart from the surface and only comes into contact with it when cleaning.

Reference numeral 53 denotes a transfer material cassette that stores a transfer material 54. The transfer material 54 is fed one by one from the transfer material cassette 53 to a paper conveyance path 56 by a half-moon-shaped paper feed roller 55. 57, in order to align the positions of the composite image formed on the transfer material 54 and the intermediate transfer body 46, the transfer material 57 is
It is a registration row for stopping and waiting the roller 4, and is in pressure contact with the driven roller 58.

59 transfers the composite image formed on the intermediate transfer body 46 to the transfer material 5
4, and rotates in contact with the intermediate transfer body 46 only when transferring the composite image to the transfer material 54.

60 is a fixing device consisting of a heat roller 61 having an internal heat source and a pressure roller 62, which applies pressure and pressure to the composite image transferred onto the transfer material 54 as the heat roller 61 and pressure roller 62 rotate. The image is fixed on the transfer material 54 by heat to form a color image.

The operation of the electrophotographic apparatus configured as described above will be described below.

The photoreceptor 31 and the intermediate transfer member 46 are each driven by a drive source (not shown), and are controlled so that their circumferential speeds are the same constant speed. Furthermore, an image forming area of the intermediate transfer body 46 is set in advance by an intermediate transfer body reference detection sensor 50 that detects an intermediate transfer body reference mark 46a for determining a reference position.
The positions of the intermediate transfer rollers 49 are adjusted so that the joints 31a do not overlap, and the intermediate transfer rollers 49 are driven in synchronization.

In this state, first, high voltage is applied to the charging wire 41 in the charger 34 connected to the high voltage power supply to cause corona discharge, and the photoreceptor 3
The surface of 1 is uniformly charged to about -700 to 800V. 7 Next, the photoreceptor 31 is rotated in the six directions of the arrow, and an exposure light beam 44 of a laser beam corresponding to a predetermined color among the plurality of color components, for example, black (B) is applied onto the uniformly charged surface of the photoreceptor 31. When irradiated, the irradiated portion on the photoreceptor 31 loses its charge and an electrostatic latent image is formed. At this time, this electrostatic latent image is placed on the photoconductor 31 at a position within the image area on the intermediate transfer body 46 that is preset by a signal from the intermediate transfer reference detection sensor 50 that detects the reference position of the intermediate transfer body 46. It is formed avoiding the seam 31a.

On the other hand, the developing device 36B containing black toner contributing to development is pushed in the direction of arrow B by the rotation of the separation cam 45E in response to the color selection signal and comes into contact with the photoreceptor 31. With this contact, toner adheres to the electrostatic latent image portion formed on the photoreceptor 31 to form a toner image, and development is completed. After the development is completed, the developing device 36B moves from the contact position with the photoreceptor 31 to the separated position by the 180 degree rotation of the contact/separation cam 45B. The toner image formed on the photoreceptor 31 by the developer 36B is transferred to the intermediate transfer member 46 for each color by applying high pressure to an intermediate transfer roller 49 placed in contact with the photoreceptor 31.

Residual toner that has not been transferred from the photoconductor 31 to the intermediate transfer body 46 is removed by the photoconductor cleaning device 38.
Further, the charge on the photoreceptor 31 from which the residual toner has been scraped off is removed by the charge eliminator 39.

Next, when the color cyan (C), for example, is selected, the separation cam 45G rotates and this time pushes the developing device 36C toward the photoreceptor 31 so that it comes into contact with the photoreceptor 31 and starts developing cyan (C). do.

In the case of a copying machine or printer that uses four colors, the above-mentioned developing operation is repeated four times in sequence, and four colors are transferred onto the intermediate transfer body 46.
Toner images of colors B, C, M, and Y are superimposed to form a composite image. The composite image formed in this way comes into contact with the intermediate transfer body 46 when the paper transfer roller 59, which has been separated until now, applies high pressure to the paper transfer roller 59, and the pressure moves the paper from the transfer material cassette 53 to the paper conveyance path 56. The images are transferred all at once onto the transfer material 54 that is fed along the direction. Subsequently, the transfer material 54 onto which the toner image has been transferred is sent to a fixing device 60, where it is fixed by the heat of the heat roller 61 and the clamping pressure of the pressure roller 62, and is output as a color image.

The residual toner on the intermediate transfer body 46 that has not been completely transferred onto the transfer material 54 by the paper transfer roller 59 is removed by the intermediate transfer body cleaning device 52. The intermediate transfer member cleaning device 52 performs the following steps until one composite image is obtained.
It is located at a distance from the intermediate transfer member 46, and after a composite image is obtained and the composite image is transferred to the transfer material 54 by the paper transfer roller 59, it comes into contact with the intermediate transfer member 46, and residual toner is removed.

With the above operations, recording of one image is completed, and a high quality color recorded image is obtained.

Note that the printer is not limited to the electrophotographic method using a laser beam in this embodiment, but may also be a thermal transfer method, an inkjet method, etc., or may be an LED method, a liquid crystal shutter type, etc., which are the same electrophotographic methods. It doesn't matter if there is.

Although this embodiment deals with a full-color printer in which gradation reproduction is important, it is of course possible to use a single-color printer. Further, in this embodiment, a method was adopted in which the color image was superimposed on the intermediate transfer member, but a method in which the color image was superimposed on a photoreceptor or a method in which it was superimposed on transfer paper may also be used.

As described in detail, the present invention sets a block consisting of a plurality of pixels on transmitted or stored image data, and within this block, a spatially predetermined priority S is set.
The image forming apparatus is configured to grow dots in order starting from the minimum recording pixel position with a high priority, and to suppress the complete growth of dots with a specific priority. It is possible to obtain high-quality recorded images with no roughness, especially in the reproduction characteristics of low-density areas and high-density areas.

[Brief Description of the Drawings] Figure 1 is a schematic diagram showing an image forming apparatus according to an embodiment of the present invention, Figure 2 is a block diagram of the gradation processing section, and Figure 3 is the time of each synchronization signal and each counter output. 4 is a state diagram of the counter output for each pixel position, 5 is a diagram explaining the contents of the gradation conversion table, 6 is a gradation conversion characteristic diagram,
FIG. 7 is a side sectional view of a laser beam printer, FIG. 8 is an explanatory diagram of the operation of photoconductor reference detection, FIG. 9 is an operation explanatory diagram of intermediate transfer member reference detection, and FIG. 10 is a block diagram of a conventional image forming apparatus. The configuration diagram, Figure 11 is the density conversion characteristic diagram, and Figure 12 is the 8
The dither threshold matrix diagram of X8, FIG. 13 is an explanatory diagram of output values in the multilevel dither method. 18... Gradation processing section

Claims (1)

[Claims] A block consisting of multiple pixels on transmitted or accumulated image data is set, and within this block, dots are sequentially printed starting from the dot corresponding to the minimum recording pixel position with the highest priority, according to a spatially predetermined priority order. What is claimed is: 1. An image forming apparatus comprising: a gradation processing section that causes dots of a specific priority to grow and suppresses complete growth of dots with a specific priority.